Explain the operation of FULL JOIN in SQL and when it is used.

The FULL OUTER JOIN operation in SQL combines rows from two tables based on a join condition, returning all rows from both tables. If there is no match, the result will contain NULLs for the columns of the table without a match.

FULL OUTER JOIN is used when you want to get a complete set of data from both tables, including both matching and non-matching rows.

Example:

SELECT A.id, A.name, B.order_id
FROM Customers A
FULL OUTER JOIN Orders B ON A.id = B.customer_id;

This will return all customers and all orders, even if a customer has no orders or an order is not linked to a customer.